Why is a bank more likely to offer you credit if you have a co-signer with good credit?

A bank is more likely to offer you credit with a co-signer who has good credit because the co-signer's strong financial history reduces the lender's risk. The co-signer essentially guarantees the loan, indicating to the bank that there is a reliable source for repayment if you default. This added security can make the bank more comfortable approving your application, even if your credit history is limited or less favorable.